1 use super::combine::CombineFields;
3 use super::lattice::{self, LatticeDir};
6 use crate::traits::ObligationCause;
7 use crate::ty::{self, Ty, TyCtxt};
8 use crate::ty::relate::{Relate, RelateResult, TypeRelation};
10 /// "Greatest lower bound" (common subtype)
11 pub struct Glb<'combine, 'infcx, 'tcx> {
12 fields: &'combine mut CombineFields<'infcx, 'tcx>,
16 impl<'combine, 'infcx, 'tcx> Glb<'combine, 'infcx, 'tcx> {
18 fields: &'combine mut CombineFields<'infcx, 'tcx>,
20 ) -> Glb<'combine, 'infcx, 'tcx> {
21 Glb { fields: fields, a_is_expected: a_is_expected }
25 impl TypeRelation<'tcx> for Glb<'combine, 'infcx, 'tcx> {
26 fn tag(&self) -> &'static str { "Glb" }
28 fn tcx(&self) -> TyCtxt<'tcx> { self.fields.tcx() }
30 fn a_is_expected(&self) -> bool { self.a_is_expected }
32 fn relate_with_variance<T: Relate<'tcx>>(&mut self,
33 variance: ty::Variance,
36 -> RelateResult<'tcx, T>
39 ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
40 ty::Covariant => self.relate(a, b),
41 // FIXME(#41044) -- not correct, need test
42 ty::Bivariant => Ok(a.clone()),
43 ty::Contravariant => self.fields.lub(self.a_is_expected).relate(a, b),
47 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
48 lattice::super_lattice_tys(self, a, b)
51 fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>)
52 -> RelateResult<'tcx, ty::Region<'tcx>> {
53 debug!("{}.regions({:?}, {:?})",
58 let origin = Subtype(self.fields.trace.clone());
59 Ok(self.fields.infcx.borrow_region_constraints().glb_regions(self.tcx(), origin, a, b))
64 a: &'tcx ty::Const<'tcx>,
65 b: &'tcx ty::Const<'tcx>,
66 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
67 debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
72 self.fields.infcx.super_combine_consts(self, a, b)
75 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
76 -> RelateResult<'tcx, ty::Binder<T>>
79 debug!("binders(a={:?}, b={:?})", a, b);
81 // When higher-ranked types are involved, computing the LUB is
82 // very challenging, switch to invariance. This is obviously
83 // overly conservative but works ok in practice.
84 self.relate_with_variance(ty::Variance::Invariant, a, b)?;
89 impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Glb<'combine, 'infcx, 'tcx> {
90 fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'tcx> {
94 fn cause(&self) -> &ObligationCause<'tcx> {
95 &self.fields.trace.cause
98 fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
99 let mut sub = self.fields.sub(self.a_is_expected);